Bottom Line:
Moreover, expression analysis revealed that the asl3 mutation severely affected the transcriptional levels of important genes associated with plastid translation machinery and photosynthesis, which may impair photosynthesis and finally led to the seedling death in asl3 mutant.These results evidenced the important role of ASL3 in the early development of rice, especially chloroplast development.Disruption of the ASL3 would lead to a defective chloroplast and seedling lethality, and affected expression levels of genes associated with chloroplast development and photosynthesis at early leaf stage of rice.

Affiliation: Development Center of Plant Germplasm Resources, College of Life and Environment Sciences, Shanghai Normal University, Shanghai, 200234 China.

ABSTRACT

Background: Pentatricopeptide repeat (PPR) proteins play essential roles in modulating the expression of organelle genes and have expanded greatly in higher plants. However, molecular mechanisms of most rice PPR genes remain unclear.

Results: In this study, a new rice PPR mutant, asl3 (albino seedling lethality3) exhibits an albino lethal phenotype at the seedling stage. This albino phenotype was associated with altered photosynthetic-pigment and chloroplast development. Map-based cloning showed that ASL3 encodes a novel rice PPR protein with 10 tandem PPR motifs, which localizes to the chloroplast. ASL3 showed tissue-specific expression, as it was highly expressed in the chlorenchyma, but expressed at much lower levels in roots and panicles. RNAi of ASL3 confirmed that ASL3 plays an essential role in the early development and chloroplast development in rice. Moreover, expression analysis revealed that the asl3 mutation severely affected the transcriptional levels of important genes associated with plastid translation machinery and photosynthesis, which may impair photosynthesis and finally led to the seedling death in asl3 mutant. These results evidenced the important role of ASL3 in the early development of rice, especially chloroplast development.

Conclusions: The ASL3 gene encoded a novel chloroplast-targeted PPR protein with 10 tandem PPR motifs in rice. Disruption of the ASL3 would lead to a defective chloroplast and seedling lethality, and affected expression levels of genes associated with chloroplast development and photosynthesis at early leaf stage of rice.

Fig7: Expression analysis of genes associated with chlorophyll biosynthesis, photosynthesis, or chloroplast development by real-time PCR. The relative expression level of each gene was normalized using Actin as an internal control. The expression level of each gene at the three-leaf stage in Jiahua1 was set as 1.0 and other samples were calculated accordingly. Error bars (SDs) are based on three independent experiments.

Mentions:
To assess the possibility that the impaired chloroplasts in asl3 mutant may be reflected at the level of related gene expression, we examined the transcription levels of genes associated with photosynthesis and chloroplast development both in the asl3 mutant and WT plant by qPCR analysis. The photosynthesis-associated transcripts of plastid genes, psbA (encoding a reaction center polypeptides) and rbcL (encoding the large subunit of Rubisco), the nuclear genes RbcS (encoding the small subunit of Rubisco, Kyozuka et al. 1993) and Cab1R (encoding the light harvesting Chla/b-binding protein of PSII), were significantly suppressed in the asl3 mutant, which may impair photosynthesis ability and finally led to the seedling lethality in mutant (Figure 7).Figure 7

Fig7: Expression analysis of genes associated with chlorophyll biosynthesis, photosynthesis, or chloroplast development by real-time PCR. The relative expression level of each gene was normalized using Actin as an internal control. The expression level of each gene at the three-leaf stage in Jiahua1 was set as 1.0 and other samples were calculated accordingly. Error bars (SDs) are based on three independent experiments.

Mentions:
To assess the possibility that the impaired chloroplasts in asl3 mutant may be reflected at the level of related gene expression, we examined the transcription levels of genes associated with photosynthesis and chloroplast development both in the asl3 mutant and WT plant by qPCR analysis. The photosynthesis-associated transcripts of plastid genes, psbA (encoding a reaction center polypeptides) and rbcL (encoding the large subunit of Rubisco), the nuclear genes RbcS (encoding the small subunit of Rubisco, Kyozuka et al. 1993) and Cab1R (encoding the light harvesting Chla/b-binding protein of PSII), were significantly suppressed in the asl3 mutant, which may impair photosynthesis ability and finally led to the seedling lethality in mutant (Figure 7).Figure 7

Bottom Line:
Moreover, expression analysis revealed that the asl3 mutation severely affected the transcriptional levels of important genes associated with plastid translation machinery and photosynthesis, which may impair photosynthesis and finally led to the seedling death in asl3 mutant.These results evidenced the important role of ASL3 in the early development of rice, especially chloroplast development.Disruption of the ASL3 would lead to a defective chloroplast and seedling lethality, and affected expression levels of genes associated with chloroplast development and photosynthesis at early leaf stage of rice.

Affiliation:
Development Center of Plant Germplasm Resources, College of Life and Environment Sciences, Shanghai Normal University, Shanghai, 200234 China.

ABSTRACT

Background: Pentatricopeptide repeat (PPR) proteins play essential roles in modulating the expression of organelle genes and have expanded greatly in higher plants. However, molecular mechanisms of most rice PPR genes remain unclear.

Results: In this study, a new rice PPR mutant, asl3 (albino seedling lethality3) exhibits an albino lethal phenotype at the seedling stage. This albino phenotype was associated with altered photosynthetic-pigment and chloroplast development. Map-based cloning showed that ASL3 encodes a novel rice PPR protein with 10 tandem PPR motifs, which localizes to the chloroplast. ASL3 showed tissue-specific expression, as it was highly expressed in the chlorenchyma, but expressed at much lower levels in roots and panicles. RNAi of ASL3 confirmed that ASL3 plays an essential role in the early development and chloroplast development in rice. Moreover, expression analysis revealed that the asl3 mutation severely affected the transcriptional levels of important genes associated with plastid translation machinery and photosynthesis, which may impair photosynthesis and finally led to the seedling death in asl3 mutant. These results evidenced the important role of ASL3 in the early development of rice, especially chloroplast development.

Conclusions: The ASL3 gene encoded a novel chloroplast-targeted PPR protein with 10 tandem PPR motifs in rice. Disruption of the ASL3 would lead to a defective chloroplast and seedling lethality, and affected expression levels of genes associated with chloroplast development and photosynthesis at early leaf stage of rice.